But where shall we look for guidance if we desire to learn how normal functional activity can be attained? Naturally, to the science which treats of the bodily functions, physiology; and we shall see in a moment that by the application of physiological principles, not only will the organs be temporarily aided in the performance of their functions, but, if continued, good physical development, that condition upon which permanent health depends, will be secured. Therefore, physiology is, as well as bacteriology, to a certain extent a science of prevention, but, in our eagerness to catch and exterminate germs, it has been pushed far into the background, though so much nearer home to us than the latter.
That physical development is an important element in the maintenance of health becomes obvious when we consider that, other things being equal, an organ performs its functions in proportion to its strength; hence, if all the organs be well developed, all the functions will be thoroughly performed.
But good physical development is the result of adequate nourisl17nent of all parts of the body, and such nourishment depends upon the proper performance of all the functions. That this does not lead us into an absurdity becomes evident when we consider that imperfectly developed organs may with assistance perform their functions efficiently, and physiology points out how this aid can be given. In consequence of this help, therefore, the organs develop and perform their functions properly with ever less assistance, and the condition of perfect health is gradually approached.
Now, if we assist the organs during childhood when they are weak, not only will much be done to secure good health during this period, but the age of maturity will be reached with a welldeveloped body, and good health, therefore, to a considerable extent assured through life. It is true that, under ordinary circumstances, a smaller body can be nourished, with weaker organs; but if as early as the sixth year a child begins to labor from five to seven hours daily the conditions are entirely changed. During childhood a large quantity of nourishment is required for growth alone, and, if a good share of this be expended in labor, it is clear that, unless something be done to compensate for this unnatural state of affairs, when the period of growth is over the body will be imperfectly developed, with very little chance of recovering the lost ground. When this is the case, the individual will be liable to be afflicted with poor health ever afterward; how often it now occurs is but too well known.
As to the means for assisting the organs in their labor, none is so powerful as muscular exercise. This agent not only plays an important part in the general nutrition of the system, having a